A General Packet Radio System (“GPRS”) is a service that provides data packet communications for mobile Global system for Mobile Communications (GSM) and time-division multiple access (TDMA) users. In addition to GSM, GPRS also provides services to other digital cellular networks, such as DCS and PCS. As is known, GPRS uses this packet-mode technique to transfer high-speed and low-speed data and signaling in an efficient manner over GSM radio networks.
GPRS provides a variety of new and unique services to mobile wireless subscribers. For example, GPRS can maintain constant voice and data communications while mobile subscribers are in transit. Subscribers also are enabled to obtain connectivity whenever needed, regardless of location and without a lengthy login session. Via a GPRS mobile telephone, a subscriber can maintain an online connection while initiating a communication, without an overhead of setting up a data call. Finally, localization enables subscribers to obtain information that is relevant to their respective current locations. For example, GPRS enables location-based services that provide information about weather, traffic, restaurants, or retail stores, based on a subscriber's location at a particular moment in time.
FIG. 1 illustrates a basic architecture of a GPRS network 100 and a data transfer route in the GPRS network. The GPRS network attempts to reuse the existing GSM network element as much as possible. In order to effectively build a packet-based mobile cellular network, some new network elements, interfaces and protocols that handle packet traffic are also required. For example, the exiting Mobile Station Switch Centers (“MSC's”) are based upon circuit-switched central-office technology and cannot handle packet traffic. Therefore, enabling GPRS on a GSM network requires the addition of two core modules, a Serving GPRS Service Node (“SGSN”) 110 and a Gateway GPRS Service Node (“GGSN”) 112, as shown in FIG. 1. GGSN 112 acts as a gateway between GPRS network 100 and an external IP network 114 such as an Internet or an x.25 Network, or another GPRS network (to facilitate GPRS roaming), and is connected with SGSN 110 via an IP-based GPRS backbone network 124. SGSN 110 is at the same level as MSC 118, and can be viewed as a “packet-switched MSC” (mobile station switch center). SGSN 110 provides packet routings to and from its service area for all MS's in that service area. SGSN 110 also detects new GPRS MS's in a given service area, processes registration of new MSs, and keeps a record of their respective locations inside the given area.
MS 102 is physical equipment used by the mobile subscribers, such as a mobile telephone or a laptop computer, which is GPRS-attached and can handle an enhanced air interface in GPRS network 100 and can packetize traffic directly. The GPRS-attached MSs may include a high-speed version of current telephones to support high-speed data access, a PDA (Packet Data Access) device with an embedded GSM telephone, and PC cards for laptop computers. All MS's profiles are preserved in home location registers (“HLR”) 120 that are accessible by SGSN 110 via local GSM MSC 118. A logical link (e.g., interface Gs) is established and maintained between a MS and a specific SGSN in each mobile network. At the end of transmission or when the MS moves out of the area of the specific SGSN, the logical link and the associated resources can be reallocated.
SGSN 110 is also coupled to a BSC (Base Station Controller) 106 via a Frame Relay connection. BSC 106 manages radio resources including Base Transceiver Station (“BTS”) 104. BTS 104 is physical equipment, such as a radio tower, that is used to transmit radio frequencies over an air interface. The BSC 106 may be connected to several BTS's. Each BTS may serve more than one MS. The BSC and BTS, as a whole, are generally referred to as a BSS (Base Station System). To be utilized in the GPRS network, BSC 106 is linked to a Packet Control Unit (“PCU”) 108 that provides a physical and logical data interface out of the BSS for packet data traffic. PCU 108 converts packet data to/from SGSN 110 into a format that can be transferred to server 116/MS 102 and implements quality of service (QoS) measurements. For example, when either voice or data traffic is originated at the mobile subscriber, it is transported over the air interface to BTS 104, and from BTS 104 to BSC 106 in the same way as in a standard GSM call. However, at the output of BSC 106, the traffic is separated. Circuit-switched voice is sent to MSC 118 via circuit-switched channels (through interface A) per standard GSM, and data is sent to SGSN 110 via PCU 108 over the Frame Relay Interface (through interface Gb) and packet-switched signaling channels (through interface Gs).
Currently, the GPRS network is designed to operate in three network operation modes (NOM1, NOM2, and NOM 3), which are shown in FIGS. 2 and 3. The network operation mode of the GPRS network is indicated by a parameter transmitted in system information messages within a cell that dictates to a GPRS MS where to listen for paging messages and how to signal towards the core network. The network operation mode represents the capabilities of the GPRS network. On NOM1 network, a MS can simultaneously establish circuit-switched (i.e., voice) and packet-switched (i.e., data) connections. On NOM2 network, the MS can remain attached to the GPRS network, but it cannot transmit or receive packet data at the same time. On NOM3 network, the MS can only establish either the circuit-switched or the packet-switched connection. That is, the MS needs to disconnect with one connection to establish the other.
There are also three classes of GPRS MS's, Class A, B, or C, for use in the above-mentioned three GPRS operation modes. These various GPRS MS's support various services. For example, a class A MS supports GPRS and other GSM services (such as SMS and voice) simultaneously, such that a class A MS can use circuit-switched voice and GPRS data services at the same time. Therefore, the class A MS can fully use the NOM1 network and is also suitable for operating in the NOM 2 and NOM 3 network. A class B MS can monitor GSM and GPRS channels simultaneously, but can only support one of these services at one time. That is, the class B MS can simultaneously register circuit-switched voice and packet-switch data services but may only use one kind of service at a time. Therefore, the class B MS can be operable in NOM 2 and NOM 3 of the GPRS network. A class C MS can only support non-simultaneous attach. The subscriber must select which service to connect to Therefore, a class C MS can make or receive calls from only the manually (or default) selective service. The service that is not selected is not reachable. The class C MS thus is only operable in NOM3 of the GPRS network.
A GPRS MS, in either class, has three states: idle, standby, and active. Data is transmitted between a MS and the GPRS network only when the MS is in the active state because in the active state, the GPRS network knows the location of the MS. However, in the standby state, the location of the MS is known only as to which routing area it is in. (Each routing area may include more than one cell within a GSM location area.) Therefore, when the network sends a packet to a MS that is in the standby state, the MS must be paged. The network first sends a paging message to a MSC within a location area where the MS is located. The MSC then sends another paging message to the SGSN. Because the SGSN knows the routing area (that is a subset of the location area) in which the MS is located, a packet paging message is then sent from the SGSN to that routing area. After receiving the packet paging message, the MS gives its cell location to the SGSN to establish the active state.
FIG. 2 is a diagram showing the first network operation mode NOM1 of the GPRS network, in which GRPS MS 201 is attached to, through BSC 202, both GPRS 204 via interfaces Gb and Gs and to other GSM services through MSC 203 via interface A, and MS 201 supports simultaneous operation of GPRS and other GSM services. As shown, in NOM1, the network sends all paging messages for GRPS MS 201 either on a Common Control Channel (CCCH) or the GPRS paging channel or on a GRPS traffic channel (if a data transfer is in progress), such as interfaces Gs and Gb. MS 201 only needs to monitor one paging channel thus allowing it to “sleep” longer. Further, the paging load is reduced since paging is performed on the routing area level.
FIG. 3 is a diagram illustrating the second and third network operation modes NOM2 and NOM3 of the GPRS network, in which GPRS MS 301 is attached to, through BSC 302, both GPRS 304 via interface Gb and other GSM services through MSC 303 via interface A and can only operate one set of services at a time. In NOM2, the network sends all paging messages for GPRS MS 301 out on the CCCH. The MS must monitor this channel even when allocated a GPRS data channel. The CS paging occurs at the location area level. In NOM 3, the network sends out the CS paging for GPRS MS 301 on the CCCH, and GPRS paging out on a Packet Paging channel (PPCH) through interface A, if allocated, or the CCCH. If PPCH are present in the cell, then MS 301 must monitor both the CCCH and the PPCH channels. The CS paging occurs at the location area level.
The primary difference between NOM1, NOM2 and NOM3 is that paging and signaling coordinate in NOM1 to occur between MSC 203 and SGSN 204. The primary difference between NOM2 and NOM3 is that in NOM 2, the GRPS MS 301 can be required to monitor different paging channels.
Currently, the MS can only be used in one operation mode of the GPRS network, based upon what service the MS subscriber registers for. That is, if the subscriber registers to use the service of NOM1, he/she cannot use the service of NOM2 or NOM3. Taking NOM 1 of FIG. 2 as an example, if the MS subscriber registers to use the first operation mode (NOM1), the subscriber can only use circuit-switched channels and packet-switched channels provided by GPRS 203 to deliver voice signals and packet data, respectively, i.e., through interfaces Gs and Gb. When interface Gs fails to operate for some reason, such as network problems and transport problems, the paging message sent from MSC 204 cannot be transmitted to the GPRS 203, causing MS 201 fails to receive calls, even though PPCH in interface A is available, because the GPRS network is not capable of switching the operation mode as needed.
Accordingly, a communications system and method that provides more flexible communications service to MS subscribers is thus desirable.